$date_fin=$_SESSION["champdatefin"];//always provided by choix_autre.php
$_SESSION["champdatefin"]="";//clean param cause 2 polls created by the same user in the same session can be affected by this param during the 2nd creation.
$sql='INSERT INTO sondage
(id_sondage, commentaires, mail_admin, nom_admin, titre, id_sondage_admin, date_fin, format, mailsonde)